1. Field of Endeavor
The present invention relates to the field of maintenance and checking of technical installations, especially in power generating plants. It relates to a drive unit for an inspection vehicle, and also to an inspection vehicle with such a drive unit.
2. Brief Description of the Related Art
Units of power generating plants, such as generators, boilers or suchlike, must be inspected and tested for their condition within the scope of the maintenance in order to reveal, and possibly to remedy, possible weak spots or defects. Such an inspection frequently necessitates access to closed-off or inaccessible areas and repeated measuring processes along the structure which is to be checked. An example of such inspections is the checking on the inner side of the rotor of a generator. For this purpose, a robot system is required, which is small enough to reach the corresponding areas and which can cover defined measuring distances.
An inspection crawler for the inspection of generators, which can be inserted in the air gap between rotor and stator, is known from U.S. Pat. No. 5,650,579. The inspection crawler includes three drive units which are equipped with driven crawler tracks and which, in a relatively spread apart manner, can be moved transversely to the direction of travel in order to fix the vehicle in the air gap. The use of this device, however, is limited to air gaps of generators.
A device for monitoring corona discharges in dynamoelectric machines is known from U.S. Pat. No. 5,252,927, in which a vehicle which is equipped with dedicated drive units is used. The actual monitoring apparatus is arranged between two drive units which are provided with crawler tracks and which have a motor-powered drive in each case. Permanent magnets, which interact with the iron of the stator core stack and press the device onto the surface which is to be covered, are arranged in a fixed manner in each case at the two ends of the drive units. With this known device, it is disadvantageous that on uneven surfaces the permanent magnets can partially lose their attracting action and the device can then fall off (especially during overhead operation). Known generator stators, for example, are sealed with a resin which is prone to drip formation on the edges of the stator core stack. Such hard-set drips, which are about 5 mm high, can represent an insurmountable obstacle for such a known device with magnetic adhesion. In practice, however, it is also disadvantageous that in each of the drive units two parallel crawler tracks are used, between which the permanent magnets are arranged. Therefore, it is the drive units in particular which cause problems in the case of the known device.